This invention relates to vehicle wheel alignment and more particularly to and improved system for replacing alignment components such as bushings or shims.
Bushings and shims are used to adjust various alignment characteristics of a vehicle, such as caster, camber and toe. For example, certain light duty trucks make use of a bushing installed in the upper control arm over the upper ball joint stud. The taper and orientation of this bushing determines the amount of change in camber, caster, or both. Some of these bushings are infinitely adjustable (within the parameters of the size of the bushing), while others have tabs which only allow the bushings to be oriented in a limited number of positions. A separate bushing is required for each wheel. Similarly, various shims, such as rear shims, are also used to adjust toe (and/or camber) of a particular wheel, and these shims come in various types (sizes, configurations) and have varying degrees of adjustability. Although the present invention is described primarily in terms of bushings, it will be appreciated that it is equally applicable to shims specifically, and alignment adjustment components in general.
For bushings that affect a change in camber only, the orientation of the bushing in the upper control arm controls the amount of change in camber. These bushings may be installed in such a position as to result in a near zero error in camber. Other bushings affect a change in both camber and caster. These latter bushings are generally manufactured with or without tabs extending from one face of the bushing, perpendicular from the shaft of the bushing. The bushings with tabs require the technician (user) to install the bushing in one of a set number of orientations, limiting the increments of change in camber and caster available. The bushings manufactured without tabs may not have this limitation.
In the case of bushings that affect both camber and caster, some residual error may result if both camber and caster cannot both be simultaneously corrected by the same bushing. In this case, a priority must be assigned to the residual error of both the camber and caster to determine the orientation of the bushing for optimum results (i.e., minimal residual error for both camber and caster). It would be desirable to display this error to the technician, so that he is aware of the error and its effect on alignment angles. It would also be desirable for the technician to be able to adjust the error for either camber or caster, as the situation warrants. The technician may want to minimize the camber error at the expense of increasing the caster error, and vice versa. There is currently alignment equipment available which gives the technician this ability for other alignment angles, such as camber and toe, but not for camber and caster with the sue of the previously discussed bushings. Such a system is disclosed in U.S. Pat. No. 5,598,357, the disclosure of which is incorporated herein by reference.
Unlike shims, tire is always a bushing installed in the vehicle. It is a required part of the upper control arm. When there is no camber or caster change induced by a bushing, it is called a "zero" bushing. These zero bushings are used in the standard bushing replacement procedure. Specifically, the standard procedure is as follows:
1. Measure the current camber/caster angles. PA1 2. In some cases, remove the wheel assembly. PA1 3. Remove the currently installed bushing and install a zero bushing. PA1 4. In some cases, replace the wheel assembly. PA1 5. Measure the change required in camber/caster and select a new bushing. PA1 6. In some cases, remove the wheel assembly again. PA1 7. Remove the zero bushing and install the new, selected bushing. PA1 8. In some cases, replace the wheel assembly a second time. PA1 9. Verify that the change in alignment caused by the new bushing is correct.
As can be readily appreciated, removing and replacing the bushing twice (and/or the wheel assembly twice), as is required by the standard procedure, takes a tremendous amount of time and results in a considerable expense.
Many times, the technician may not have the exact bushing required in stock. In that case, it would be desirable to select another size bushing from stock that would provide minimal residual errors in camber and caster. There are charts available for this purpose, but those are generally hard to read and they have some "holes" (combinations of bushings in stock versus optimal bushings for which the charts have no suggestion). The same situation exists for shims.
The technician is often forced to guess as to correct orientation of a bushing in the installation. Although the charts provide an angular orientation at which the bushing is to be installed, it is not always altogether clear how the particular bushing is to be rotated to the desired orientation. If would be helpful if some means were available to eliminate errors in the actual orientation of the bushing during installation.